Thermal management composite heat shield

ABSTRACT

A thermal management system and methods for use are disclosed. The thermal management system comprises a shield portion and a dissipation portion. The shield portion may comprise a hot side skin, a conduction layer, an insulation layer, and a cool side skin. The dissipation portion may comprise a fin array. Heat absorbed by the shield portion is partially or fully conducted to the dissipation portion for transfer to the ambient environment. The thermal management system may be employed as an aircraft wheel heat shield, an automotive brake heat shield, a gas turbine heat shield, an electronic heat sink, and in various other applications where heat shielding and/or heat transfer are desirable.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and is a divisional of U.S. patentapplication Ser. No. 12/692,181, filed on Jan. 22, 2010, entitled“THERMAL MANAGEMENT COMPOSITE HEAT SHIELD.” The '181 application claimspriority to and the benefit of U.S. Provisional Application Ser. No.61/149,178, filed on Feb. 2, 2009, entitled “THERMAL MANAGEMENTCOMPOSITE HEAT SHIELD” Both the '181 application and the '178application are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The present invention generally relates to thermal management, and moreparticularly, to thermal transmission and thermal shielding in brakesystems.

BACKGROUND OF THE INVENTION

Various mechanical and/or electrical systems, such as braking systems(and in particular, aircraft braking systems), typically generatesignificant heat. For example, significant heat is generated when thekinetic energy of a vehicle is converted to thermal energy. To helpcompensate for the increased temperatures, individual brake components(e.g., brake pads, rotors, and the like) may be configured to toleratehigh temperatures.

For example, an aircraft brake pad friction component may absorb asignificant amount of heat during braking (e.g., resulting in a brakepad friction component temperature exceeding 1000 degrees Fahrenheit),while other components in the vicinity of the brakes, such as analuminum wheel, may be less heat tolerant. Accordingly, brake padfriction components gradually dissipate heat while the aircraft isparked on the ground. The ability to expeditiously cool the brake padfriction components may influence how quickly the aircraft is allowed to“turn around” and complete another takeoff/landing cycle. In thisregard, cooling a brake pad friction component or other structuralcomponents more rapidly may enable higher utilization of an aircraft orother vehicle.

Typical conventional attempts to address such heat concerns and decreasecooling time involve bringing a cooling medium (e.g., air driven byelectric fans) to the source of heat in order to transfer the heat away.However, bringing the cooling medium to the heat source is often notpractical and/or may be expensive.

Accordingly, improved thermal management techniques and components mayreduce and/or eliminate the need for bulky, heavy, and/or complicatedadditional safety and/or cooling systems. Moreover, a need exists toprevent heat generated by a braking system from reaching otherheat-sensitive components.

SUMMARY OF THE INVENTION

A thermal management system and methods for use are provided herein. Invarious embodiments, the thermal management system comprises a shieldportion and a dissipation portion. Heat absorbed by the shield portionmay be conducted to the dissipation portion for transfer to the ambientenvironment. The thermal management system may be employed in anaircraft wheel heat shield, an automotive brake heat shield, a gasturbine heat shield, an electronic heat sink, and in various otherapplications where heat shielding and/or heat transfer are desirable.

In various embodiments, the shield portion comprises a hot side skin, aconduction layer, an insulation layer, and a cool side skin, while thedissipation portion may comprise a fin array and an optional main body(which may itself by incorporated into the fin array). The conductionlayer may comprise a planar carbon fiber structure or graphite flakeconfigured with an in-plane thermal conductivity from about 100 wattsper meter-Kelvin to greater than about 2000 watts per meter-Kelvin. Theinsulation layer may comprise a planar nanoporous structure configuredwith a through-plane thermal conductivity of less than about 25 wattsper meter-Kelvin.

In various embodiments, a thermal management system may be manufacturedby impregnating a sheet of carbon fiber with a resin to form a firstlayer, infiltrating a carbon felt with nanoporous material to form asecond layer, and coupling the first layer and second layer to form anassembly. The method may further comprise pyrolyzing the assembly at atemperature between about 900 degrees Celsius and 1350 degrees Celsius,and then annealing the assembly at a temperature between about 1800degrees Celsius and 3000 degrees Celsius. The assembly may then becoated with a coating material configured to reduce porosity of theassembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a thermal management system in accordance with anembodiment;

FIG. 2 illustrates a shield section of a thermal management system inaccordance with an embodiment;

FIG. 3 illustrates a dissipation section of a thermal management systemin accordance with an embodiment;

FIG. 4 illustrates a method for creating a thermal management system inaccordance with an embodiment; and

FIG. 5 illustrates a thermal management system configured in an aircraftwheel well in cross section;

FIG. 6 illustrates a thermal management system configured in an aircraftwheel well; and

FIG. 7 illustrates a dissipation section.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings, which show exemplary embodiments by way ofillustration and its best mode. While these exemplary embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the invention, it should be understood that other embodimentsmay be realized and that logical, chemical and mechanical changes may bemade without departing from the spirit and scope of the invention. Thus,the detailed description herein is presented for purposes ofillustration only and not of limitation. For example, the steps recitedin any of the method or process descriptions may be executed in anyorder and are not necessarily limited to the order presented. Moreover,many of the functions or steps may be outsourced to or performed by oneor more third parties. Furthermore, any reference to singular includesplural embodiments, and any reference to more than one component or stepmay include a singular embodiment or step. Also, any reference toattached, fixed, connected or the like may include permanent, removable,temporary, partial, full and/or any other possible attachment option.Additionally, any reference to without contact (or similar phrases) mayalso include reduced contact or minimal contact.

In various embodiments, a thermal management system is any device and/orstructure configured to reduce, restrict and/or eliminate the flow ofheat to a desired area. Moreover, a thermal management system may alsoincrease the flow of heat to another desired area. For example, throughthe use of a thermal management system, all or a portion of the heatgenerated by a brake assembly located within an aircraft wheel or tiremay be prevented from reaching the wheel, and all or a portion of theheat may be transferred to an area exposed to an ambient airstream inorder to achieve faster cooling of various brake assembly components.

With reference now to FIG. 1, and in accordance with various exemplaryembodiments, a thermal management system 100 comprises shield section110 and dissipation section 130. As described in further detail below,shield section 110 further comprises hot side skin 102, conduction layer104, insulation layer 106, and cool side skin 108. Dissipation section130 further comprises main body 132 and fin array 134. Shield section110 and dissipation section 130 are operatively coupled to allow heattransfer between them.

With reference now to FIG. 2, shield section 110 comprises any suitablestructure configured to provide a low degree of thermal conductivity ina first direction and a high degree of thermal conductivity in a seconddirection. Moreover, shield section 110 may comprise a mechanicallysolid and strong structure. In an exemplary embodiment, shield section110 is a brake heat shield comprised of hot side skin 102, conductionlayer 104, insulation layer 106, and cool side skin 108. Moreover,shield section 110 may comprise any suitable number, type, size, andconfiguration of layers and/or materials to fully or partially provide adesired thermal conductivity differential and/or mechanicalcharacteristics. For example, conduction layer 104 may be thicker than,the same thickness as, or thinner than insulation layer 106 in order toprovide desired thermal conductivity characteristics for shield section110.

With continued reference to FIG. 2, and in accordance with an exemplaryembodiment, hot side skin 102 comprises any suitable structureconfigured to provide a high strength structural layer to shield section110. Hot side skin 102 is coupled to conduction layer 104, and fully orpartially transmits heat received from an external source to conductionlayer 104. In various embodiments, hot side skin 102 may comprise ametal, a composite, a ceramic, and/or the like. In an exemplaryembodiment, hot side skin 102 comprises silicon carbide reinforced witha high conductivity carbon fiber. The carbon fiber may have anyappropriate characteristics, for example, any suitable diameter,spacing, density, alignment, length, and the like. Moreover, the siliconcarbide offers superior oxidation resistance when compared with atypical carbon matrix. Further, a final processing step utilizingpolysilizane resin infiltration may be employed in order to create astrong, dense outer surface layer.

Hot side skin 102 may further comprise a woven mat. The woven mat may beany weave configuration selected to give a desired characteristic, suchas thickness, surface structure, and the like. For example, thereinforcing carbon fiber may comprise a woven sheet of low-moduluspitch-based carbon fibers, for example Amoco P55, P30X, or K-1100,Nippon XNC 25, XN50A, XN70A, or XN80A, Thornel® K-800x, or Cytek C-100.Moreover, any suitable reinforcing material may be used.

In various embodiments, hot side skin 102 exhibits a tensile strength offrom about 200 MPa to about 400 MPa at room temperature. Hot side skin102 also exhibits a flexural strength of from about 150 MPa to about 350MPa at room temperature. In an exemplary embodiment, hot side skin 102exhibits a tensile strength of about 300 MPa at room temperature and aflexural strength of about 250 MPa at room temperature.

Hot side skin 102 may further comprise a solid surface or any othermaterial configured to be resistant to penetration by foreign materials.For example, hot side skin 102 may comprise CMC (ceramic matrixcomposite forming) polymer.

In various embodiments, hot side skin 102 comprises a carbon matrixreinforced with carbon fiber textile or a CMC comprising polysialatematrix reinforced with carbon fiber textile. In embodiments having a CMChot side skin, the CMC may comprise an aluminosilicate CMC based onpolysilate resin or a silicon carbide (“SiC”) CMC based on polysilazaneresin. In embodiments having a carbon composite hot side skin, thecarbon composite may be based upon pitch resin.

In embodiments having an aluminosilicate CMC based on polysilate resin,the polysilate matrix may be formed at pressures of from about 8 MPa toabout 12 MPa, more preferably from about 9 MPa to about 11 MPa, and mostpreferably at about 10 MPa. An aluminosilicate CMC based on polysilateresin may be cured at temperatures less than about 150° C. and aboveabout 0° C.

In embodiments having a SiC CMC based on polysilazane resin, any methodof infiltrating or densifying may be employed to produce the final CMC.For example, vacuum resin transfer or slurry casting may be used todensify polysilazane resin with SiC. Polysilizane undergoes pyrolysisbetween about 750° C. to about 1400° C.

With continued reference to FIG. 2, and in accordance with an exemplaryembodiment, conduction layer 104 comprises any structure configured withcomparatively high in-plane thermal conductivity and comparatively lowthrough-plane (i.e., substantially normal to plane) thermalconductivity. For example, conduction layer 104 may comprise a fiber, afoam, a flake, a nanoparticle, and/or other structure configured toachieve desired thermal conductivity characteristics. In an exemplaryembodiment, conduction layer 104 is coupled to hot side skin 102 and toinsulation layer 106. By coupling conduction layer 104 to hot side skin102, heat may be transferred to conduction layer 104 from hot side skin102 such that the heat is conducted along the high thermally conductiveplane of conduction layer 104. Conduction layer 104 may also extend atleast partially into dissipation section 130. Moreover, conduction layer104 may be configured to reduce hot spots resulting from unevenapplication of thermal energy to conduction layer 104, for example byspreading heat via in-plane thermal conduction.

In an exemplary embodiment, conduction layer 104 comprises a generallyplanar graphite fiber reinforced composite material. Pitch-based carbonfibers may be utilized to provide a high strength and lightweightconfiguration. Various parameters (e.g., the cross-section of thereinforcing fibers, the reinforcing orientation, and the like) may besuitably varied to achieve a desired level of in-plane thermalconductivity and/or a desired level of through-plane thermalconductivity.

Conduction layer 104 may comprise a three-dimensional woven compositecomprised of silicon carbide and graphite fiber. Conduction layer 104may comprise a structure having an intermediate grade in all directions(e.g., Amoco P55 or similar). Conduction layer 104 may also comprise astructure having a high thermal conductivity in the high fiber densitydirection (e.g., Amoco K-100 or similar). The woven mat may be any weaveconfiguration selected to achieve a desired thickness, surfacecharacteristic, and the like. For example, a woven sheet of low-modulus,pitch-based carbon fibers (e.g., Amoco P30X, Nippon XNC25, and the like)may be impregnated with a selected resin, such as by a pressure rollingprocess wherein the sheet is squeezed between opposing rollers. Resinmay be applied to the sheet before rolling and/or during rolling. Thepost-rolling sheet may be handled, formed, molded, and otherwise shapedand/or configured after exiting the rolling process. The quantity ofresin applied to the sheet may be varied to achieve a desired stateafter pyrolysis (i.e., after heating the material in the absence ofoxygen).

During pyrolysis, much of the resin is burned off, and much of theremaining resin is converted to carbon. In an exemplary embodiment, thequantity of resin residue is approximately 20% of the original resin. Inanother exemplary embodiment, the quantity of resin residue is fromabout 3% to about 11% of the combined volume of composite fiber andresin structure. Carbon residue remaining after pyrolysis of the resintypically does not offer the high conductivity properties of the carbonfibers. As such, this residue may be minimized to an amount sufficientto provide a desired level of thermal conductivity, yet maintain adesired level of structural stability of conduction layer 104.

Conduction layer 104 may also comprise thermal pyrolytic graphite (TPG),such as TPG manufactured from thermal decomposition of hydrocarbon gasin a high temperature chemical vapor deposition reactor. In thisconfiguration, conduction layer 104 may comprise highly orientedcrystals in an in-plane structure. Moreover, conduction layer 104 mayexhibit an in-plane thermal conductivity from about 1300 w/mK to about1700 w/mK, and may exhibit a through-plane thermal conductivity fromabout 5 w/mK to about 25 w/mK.

In various exemplary embodiments, conduction layer 104 may be partiallyor fully foam reinforced. In an exemplary embodiment, conduction layer104 comprises high conductivity pitch-derived graphite foam. Conductionlayer 104 may thus exhibit in-plane thermal conductivity in excess of170 w/mK, while having a density of about 0.6 grams per cubiccentimeter.

Conduction layer 104 may also comprise a high conductivity filler. In anexemplary embodiment, conduction layer 104 comprises a carbon nanofiberfiller having a fiber diameter from about 70 nanometers to about 200nanometers, and a fiber length from about 50 microns to about 100microns (e.g., Pyrograf®-III or similar). In another exemplaryembodiment, conduction layer 104 comprises a discontinuous fiber (e.g.,ThermalGraph® DKA X or similar). Conduction layer 104 may also comprisea fibrous or foam material impregnated with carbon nanotubes. Conductionlayer 104 may incorporate various forms of nanotubes, such as spunthreads, felted mats, and the like.

In various exemplary embodiments, conduction layer 104 comprises aseries of layered materials. For example, conduction layer 104 maycomprise a first sub-layer having a high thermal conductivity in a firstdirection X co-planar to conduction layer 104, and a second sub-layerhaving a high thermal conductivity in a second direction Y, where Y isalso co-planar to conduction layer 104 but normal to first direction X.In this manner, conduction layer 104 may achieve desirable thermalconductivity properties while also achieving other desiredcharacteristics, for example thickness, weight, strength, and the like.

In various embodiments, a conductive layer may comprise molded graphiteflakes or particles with mesophase pitch resin. Mesophase carbon pitch(liquid crystal pitch) is typically partially pyrolyzed such that theconversion to graphite is only partial. Continued pyrolysis results ingraphitization of the mesophase pitch and may be used as a matrixmaterial to bind carbon flakes or fibers. The use of molded graphiteflakes or particles with mesophase pitch resin may result in a finalpart comprising a highly oriented carbon graphite composite material.Such a final part may be formed by a mixing a mesophase pitch withgraphite flakes, rolling and/or pressing the mixture to align thegraphite flakes to form a part body, carbonizing the part body andgraphitizing the part body. Carbonizing may be performed between about1000° C. to about 1500° C. Graphitizing may be performed between about2000° C. and about 2800° C. The crystal structure of the resultantgraphite may form a thermally anisotropic carbon material, with thermal(and electrical) conductivity within the plane that may be much higherthan thermal (and electrical) conductivity through the plane. Thethermal conductivity of such a thermally anisotropic carbon material maybe suitable for use as a conductive layer, as disclosed herein.

Flake graphite is a naturally occurring form of graphite that istypically found as discrete flakes ranging in size from about 50micrometers to about 800 micrometers in diameter and from about 1micrometer to about 150 micrometers thick. Such a form of graphite has ahigh degree of crystallinity, high thermal and electric conductivity,and suitable molding characteristics for use as a conductive layer.Purified flake graphite carbon is available in purities ranging from99.7-99.9% (LOI), and sizes from about 2 microns to about 800 microns.Thermal treatment of the raw graphite materials at temperatures up toabout 2800° C. is preferred so that at least a portion of the volatilecompounds, gases and impurities are vaporized.

The formation of molded graphite flakes or particles with mesophasepitch resin may occur using any suitable method now known or hereinafterdeveloped. It is believed that graphite flake size may affect thermalconductivity of the final part body. For example, it is believed thatlarger graphite particles provide a higher thermal conductivity of thefinal part body. As described above, graphite flake size may range fromabout 2 microns to about 800 microns, although it is preferred thatgraphite flake size is less than about 200 microns. Further, it isbelieved that thermal conductivity increases as a function of final partdensity, graphite purity, and degree of graphitization. Thus, particlesize, final density, purity, and graphitization may be adjusted toachieve various thermal conductivity properties of a conductive layer.

A conductive layer comprising molded graphite flakes or particles withmesophase pitch resin may be formed in a configuration having a highaspect ratio. For example, an aspect ratio of about 10:100 or higher maybe appropriate for use in various embodiments.

Conduction layer 104 may also comprise molded exfoliated graphiteparticulate with a polysialate binder, a polysilazane binder, and/or apitch carbon binder. In an exemplary embodiment, molded exfoliatedgraphite particulate using a polysialate binder is used in embodimentshaving a hot side skin comprising an aluminosilicate CMC. In anexemplary embodiment, molded exfoliated graphite particulate using apolysilazane binder is used in embodiments having a hot side skincomprising a SiC CMC. In an exemplary embodiment, molded exfoliatedgraphite particulate using a pitch carbon binder is used in embodimentshaving a hot side skin comprising a carbon composite. However, anycombination of hot side skin and conduction layer is contemplatedherein.

With continued reference to FIG. 2, and in accordance with an exemplaryembodiment, insulation layer 106 comprises any structure configured withcomparatively low thermal conductivity, particularly in thethrough-structure direction. For example, insulation layer 106 maycomprise a fiber, a foam, and/or other structure configured to achievedesired thermal conductivity characteristics. Insulation layer 106 maybe coupled to conduction layer 104 and to cool side skin 108.

In various exemplary embodiments, insulation layer 106 partially orfully comprises an aerogel, for example a low-density, open-cell foamhaving a fine cell size. Aerogels typically exhibit continuous porosityand a microstructure comprised of interconnected colloidal-likeparticles or polymeric chains with characteristic diameters from about30 nanometers to about 5 micrometers. The microstructure imparts highsurface area to aerogels, for example, from about 350 square meters pergram to about 1000 square meters per gram.

In various embodiments, aerogels may be used in conjunction with carbonfoam or felt. For example, a carbon felt or foam/aerogel insulationlayer may be used in conjunction with a conductive layer comprising amolded exfoliated graphite particulate using a polysilazane binder and ahot side skin comprising a SiC CMC. Also in various embodiments, acarbon felt or foam/aerogel insulation layer may be used in conjunctionwith a conductive layer comprising a molded exfoliated graphiteparticulate using a pitch carbon binder and a hot side skin comprising acarbon composite.

In an embodiment, a nanoporous carbon aerogel may be synthesized with asolution of resorcinol, formaldehyde, catalyst, and water. Gelation ofthe solution and aging provide the nanostructured network. The solvent(water) in the pores is replaced by acetone and the gel is subcriticallydried. The resulting resorcinol-formaldehyde aerogel may be convertedinto a pure carbon aerogel by pyrolysis. The pore sizes within thecarbon aerogel may be tailored, for example, from about 30 nanometers toabout 5 micrometers, by suitable modification of the processingparameters. The nanoporous structure of the aerogel reduces gaseousthermal conduction as well as thermal transport.

In various embodiments, insulation layer 106 comprises a series oflayered materials. For example, insulation layer 106 may comprise afirst sub-layer having a desired convective thermal conductivity, and asecond sub-layer having a desired radiative thermal conductivity. Inthis manner, a desired net thermal conductivity of insulation layer 106may be obtained.

In an exemplary embodiment, insulation layer 106 comprises a generallyplanar fiber structure configured as a structural reinforcement for anaerogel insulator. In this configuration, an impregnated aerogelinsulator occupies small pores between the carbon fibers, reducingconvective and/or radiative heat transfer. A desirable level ofinsulation is thus achieved, as the transfer of heat by radiationthrough the pores dominates at high temperatures, and the aerogelinsulator reduces this transfer. In an embodiment, insulation layer 106has a density of about 0.07 grams per cubic centimeter. Moreover,insulation layer 106 may also be configured to withstand an appliedtemperature in excess of 4000 degrees Fahrenheit (2204 degrees Celsius).

In another embodiment, insulation layer 106 comprises carbon foamconfigured as a structural reinforcement for an aerogel insulator. Ingeneral, the thermal conductivity of unfilled carbon foam increasesrapidly with temperature, as radiation through the porous structurebecomes the dominant mode of heat transfer. Thus, an aerogel insulatormay be applied to occupy the pores of the carbon foam, reducing heattransfer. Moreover, a silicon carbide coating, such as a coating appliedto the carbon foam via a polymeric precursor, may partially or fullyserve as a ligament coating to the carbon foam. Such a configuration mayincrease the compressive strength of the carbon foam by up to about250%, while reducing the thermal conductivity by about 5%.

In yet another embodiment, insulation layer 106 comprises a felt ofcarbon fibers infiltrated by a nanoporous sol-gel derived carbonaerogel. In this configuration, cracks caused by the shrinkage of thegel upon drying may be present in the composite material. These cracksmay be up to about 0.5 mm in size. Due to the anisotropic nature of thefelt (e.g., the felt may comprise a pinned stack of fiber mats), thethermal conductivity of the composite structure is anisotropic. Theanisotropy of the thermal conductivity (i.e., the ratio of thecomponents perpendicular to and parallel to the felt surface) may beabout two (2) under vacuum conditions. The density of the carbon fiberfelt may be about 100 kilograms per cubic meter, and the density of thefelt-aerogel composite may be about 230 kilograms per cubic meter.

In further embodiments, insulation layer 106 may comprise a polysialatesyntactic foam. Such embodiments may also include a conductive layercomprising molded exfoliated graphite particulate using a polysialatebinder and having a hot side skin comprising an aluminosilicate CMC.

With continued reference to FIG. 2, and in accordance with an exemplaryembodiment, cool side skin 108 comprises any suitable structureconfigured to provide a high strength structural layer to shield section110. In various embodiments, cool side skin 108 is coupled to insulationlayer 106. Cool side skin 108 may comprise a metal, a composite, aceramic, and/or the like. In an exemplary embodiment, cool side skin 108comprises silicon carbide reinforced with a carbon fiber. The siliconcarbide offers superior oxidation resistance when compared with atypical carbon matrix. Further, a final processing step utilizingsilicon resin infiltration may be employed in order to create a strong,dense outer surface layer.

For example, cool side skin 108 may comprise a polysialate matrixreinforced with silica or borosilicate fiber textile, a polysilazanematrix reinforced with silica fiber textile or borosilicate glass,and/or a carbon matrix reinforced with carbon fiber textile. In variousembodiments, a cool side skin comprising polysialate matrix reinforcedwith silica or borosilicate fiber textile may be used in conjunctionwith an insulation layer comprising polysialate syntactic foam, aconductive layer comprising molded exfoliated graphite particulate usinga polysialate binder and a hot side skin comprising an aluminosilicateCMC. In various embodiments, a cool side skin comprising polysilazanematrix reinforced with silica fiber textile may be used in conjunctionwith an insulation layer comprising carbon felt or foam/aerogel inconjunction with a conductive layer comprising a molded exfoliatedgraphite particulate using a polysilazane binder and a hot side skincomprising a SiC CMC. In further embodiments, a cool side skincomprising carbon matrix reinforced with carbon fiber textile may beused in conjunction with an insulation layer comprising carbon felt orfoam/aerogel, a conductive layer comprising exfoliated graphiteparticulate with pitch carbon binder and a hot side skin of carbonmatrix reinforced with carbon fiber textile.

In various embodiments, cool side skin 108 may optionally comprise acoating. For example, cool side skin 108 may be coated with polysialateor polycarbosilate, preferably in embodiments comprising a hot side skinof carbon matrix reinforced with carbon fiber textile.

With reference now to FIG. 3, dissipation section 130 may comprise anysuitable structure configured to fully or partially transfer heat fromthermal management system 100 into the ambient environment. For example,dissipation section 130 may receive thermal energy from conduction layer104 of shield section 110. Dissipation section 130 may also receivethermal energy from other portions of shield section 110 and/or from anexternal heat source (e.g., a brake assembly). In accordance with anembodiment, dissipation section 130 comprises a composite materialstructured as optional main body 132 and fin array 134.

Main body 132 may comprise any suitable structure configured to allowheat transfer from shield section 110 to fin array 134. Moreover, mainbody 132 may be at least partially or fully integrated into fin array134 and, in various embodiments, no main body is present. Main body 132and/or fin array 134 may individually or collectively be referred to asa heat dissipation apparatus.

Fin array 134 may comprise any suitable structure configured to allowpartial or full heat transfer from thermal management system 100 intothe ambient environment. In various exemplary embodiments, fin array 134comprises a carbon-based composite material formed by slitting acomposite fabric and weaving the fabric strips into an interlaced,“basket weave” pattern. However, the fabric may be interlaced in variousalternative arrangements in order to achieve various desiredcharacteristics, such as air flow, structural strength, heat dissipationcapability, and the like. In accordance with an embodiment, fin array134 comprises a series of carbon fins extending outward from main body132.

Fin array 134 may be formed by creating openings on an exposed end ofdissipation section 130. In this manner, the circulation of air or othercooling material may be allowed in and/or around the highly conductivefibers. Such openings may be formed in any suitable manner, for example,during the fiber weaving process, or by a separate piercing operation.Various characteristics of fin array 134 (e.g., fin spacing, fin height,fin length, temperature differential between fin and ambientenvironment, and the like) may be varied in order achieve a desireddegree of heat transfer from dissipation section 130 to the ambientenvironment.

Additionally, in various embodiments, fin array 134 is placed in astagnant fluid (e.g., calm air or similar). The density gradient createdby the presence of the hot fin surface gives rise to buoyancy drivenflow along each fin. In such embodiments, this self-induced flow may bethe principal means by which fin array 134 transfers heat to the ambientenvironment. Fin array 134 may also desirably be exposed to an airstreamin order to move a larger amount of air or other cooling fluid over finarray 134. Moreover, fin array 134 may fully or partially transfer heatto the ambient environment in any suitable manner.

A thermal management system 100 may be created via various methods. Forexample, thermal management system 100 may be welded, bonded, cut,machined, molded, pressed, sintered, cured, heated, annealed, dried,infiltrated, and/or otherwise shaped and/or formed.

In an exemplary embodiment, and with reference now to FIG. 4, a wovensheet of low modulus pitch carbon fibers is impregnated with anappropriate resin [step 402]. The carbon sheet is pierced, slit, wovenand/or otherwise formed and/or shaped to form fins and openings [step404]. One or more fin sheets are placed in parallel and cured at atemperature of about 225 degrees Celsius to about 325 degrees Celsius tobond the fin sheets together [step 406]. For example, the fin sheets maybe warm pressed using a 10 ton press to produce a partially cured part.

An organic aerogel precursor composition is infiltrated into areticulated vitreous carbon precursor felt or foam. The infiltratedorganic aerogel precursor composition is cured and dried. A conductingparticulate is infiltrated, and the aerogel is encapsulated within awoven cloth and impregnated with CMC polymer [step 408].

The assembly is pyrolyzed by heating the cured structure in an inertatmosphere or vacuum to a temperature from about 900 degrees Celsius toabout 1350 degrees Celsius for a time from about 30 minutes to about 5hours [step 410].

The pyrolyzed assembly is densificated to achieve an overall bulkdensity from about 1.7 grams per cubic centimeter (g/cm³) to about 2.2g/cm³ at a temperature from about 900 degrees Celsius to about 1100degrees Celsius [step 412]. The assembly is then annealed at atemperature from about 1800 degrees Celsius to about 3000 degreesCelsius to increase desirable physical properties of the structure [step414]. For example, annealing may further order the structure of thematrix carbon and the fiber carbon to increase the in-plane and/orthrough-plane components of thermal conductivity by an order ofmagnitude or more. Annealing may also improve the oxidative stability ofthe structure.

The assembly may be infiltrated with coating materials configured toreduce porosity and/or improve rigidity [step 416]. Molten silicon maybe infiltrated into the open pores of the sintered body at a temperatureof about 1300 degrees Celsius to about 1800 degrees Celsius in a vacuumor an inert atmosphere.

Polymeric pre-ceramic precursors may also be provided and fired. Forexample, these precursors may yield an amorphous or crystalline betasilicon carbide when fired to a low or high temperature, respectively.Exemplary precursors include Starfire® 1, an allylhydridopolycarbosilane(AHPCS), and VL202, a polysilazane. The precursors may also be modifiedwith the addition of other compounds, for example butoxide in an amountof from about 1% to about 3%. The precursors may be infiltrated bydilution with a solvent. The precursors may also be infiltrated byvacuum infiltration within a mold. The structure is then cured at a lowtemperature to release the volatile organic compounds, followed byrepeated infiltrations before firing at an elevated temperature.

In an embodiment, thermal management system 100 is configured as anaircraft wheel heat shield in order to reduce the flow of heat from thebrakes to the wheel. In another embodiment, thermal management system100 is configured as a heat shield within a brake assembly in order toreduce heat flow from brake friction components to other parts of thebrake assembly. Moreover, thermal management system 100 may beconfigured for use with electronic components, aircraft chassiscomponents, brake pads, brake rotors, gas turbines, householdappliances, automotive components, and the like. Thermal managementsystem 100 may be employed in any suitable configuration, application,or industry wherein heat may be partially or fully transmitted from afirst location to a second location, and/or partially or fully generatedat a first location and insulated from a second location.

In an exemplary embodiment, thermal management system 100 is configuredas a generally planar structure having a thickness of between aboutone-eighth (⅛) inch to about one-fourth (¼) inch, having a through-planethermal conductivity less than about 2 watts per meter-Kelvin (w/mK),and having an in-plane thermal conductivity greater than about 100 w/mK.

In another embodiment, thermal management system 100 is configured foruse with gas turbine fuel nozzles. In this embodiment, thermalmanagement system 100 allows for heat transfer from the nozzles to theambient environment. In this manner, various operational drawbacks, suchas buildup of coke on the fuel nozzles, may be reduced and/oreliminated.

In a further embodiment, thermal management system 100 is configured foruse with an aircraft brake. In this embodiment, thermal managementsystem 100 allows for heat transfer from the aircraft brake to theambient environment. In this manner, the operating temperature of anaircraft brake may be reduced.

In yet another embodiment, the thermal management system is configuredfor use as a heat sink for an integrated circuit. In this embodiment,the thermal management system is coupled to an integrated circuit, forexample a general purpose microprocessor (e.g., Intel Pentium®, AMDAthlon®, and the like). Heat generated by the integrated circuit ispartially or fully transmitted through thermal management system 100 andradiated to the ambient environment. Because the thermal conductivity ofthermal management system 100 may exceed that of traditional materials(e.g., steel, copper, aluminum, and the like) by an order of magnitudeor more, the size and/or expense of integrated circuit cooling systemsmay be greatly reduced.

With reference to FIG. 5, an exemplary thermal management system 500 isillustrated in cross section in an aircraft wheel well. Thermalmanagement system 500 comprises dissipation section 520 (also referredto as heat dissipation apparatus) and shield section 518. Shield section518 may comprise hot side skin 512, conductive layer 510, insulationlayer 508, and cool side skin 506. In such a configuration, hot sideskin 512 is positioned to transfer heat 524 from inside wheel well 522to conductive layer 510. Conductive layer 510, having in-plane thermalconductivity properties consistent with those described above, ispositioned to conduct heat to dissipation section 520. Insulation layer508 is positioned to assist in the prevention of heat migration (forexample, the migration of heat 524) to wheel well 522. Cool side skin506 is positioned as an interface to wheel well 522. In such aconfiguration, thermal management system 500 provides wheel well 522 adegree of protection from excess heat, such as heat 524.

Dissipation section 520 comprises a fin array 502 and main body (notshown, but integrated into fin array 502). The main body is thermallycoupled to shield section 518, for example, by thermal coupling withconductive layer 510. Thermal coupling may be accomplished via anysuitable means, for example, by contacting a portion of conductive layer510 with a portion of the main body or, in various embodiments, with finarray 502 directly. In various embodiments, thermal coupling may occur,at least partially, through other objects. For example, in variousembodiments, bolt 516 may act to transfer thermal energy to the mainbody and/or fin array 502, although in various embodiments bolt 516preferably does not act to thermally couple shield section 518 with finarray 502 and/or the main body.

Fin array 502 is configured to allow air to flow through the fin arrayas shown by direction 514. Air flowing in direction 514 may act toremove heat from fin array 502 and effect heat transfer from fin array502 to the ambient environment. Thus, thermal energy from inside thewheel well may travel through hot skin 512 to conductive layer 510,through conductive layer 510 to the main body and/or fin array 502, andbe released into the ambient environment.

With reference to FIG. 6, thermal management system 600 is showndisposed in wheel well 602. Shield section 606 is illustrated within thelining of the wheel well, having the hot side skin facing the interiorof wheel well 602, above a conductive layer, insulation layer, and coolside skin layer (not shown). Fin array 604 is configured to thermallycouple to shield section 606, so that heat may be conducted through finarray 604 and transferred to the ambient environment,

With reference to FIG. 7, fin array 700 is shown. Fin array 700 haslateral fins 704 and longitudinal fins 702. Although lateral fins 704and longitudinal fins 702 are shown at substantially right angles to oneanother, other geometric configurations are contemplated herein. Theconfiguration of lateral fins 704 and longitudinal fins 702 provideextended surface area for the transfer of heat from the fin array to theambient environment.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any elements that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as critical, required, or essentialfeatures or elements of the invention. The scope of the invention isaccordingly to be limited by nothing other than the appended claims, inwhich reference to an element in the singular is not intended to mean“one and only one” unless explicitly so stated, but rather “one ormore.” Moreover, where a phrase similar to “at least one of A, B, and C”is used in the claims, it is intended that the phrase be interpreted tomean that A alone may be present in an embodiment, B alone may bepresent in an embodiment, C alone may be present in an embodiment, orthat any combination of the elements A, B and C may be present in asingle embodiment; for example, A and B, A and C, B and C, or A and Band C. Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to be construed under theprovisions of 35 U.S.C. 112, sixth paragraph, unless the element isexpressly recited using the phrase “means for.” As used herein, theterms “comprises”, “comprising”, or any other variation thereof, areintended to cover a non-exclusive inclusion, such that a process,method, article, or apparatus that comprises a list of elements does notinclude only those elements but may include other elements not expresslylisted or inherent to such process, method, article, or apparatus.

What is claimed is:
 1. A thermal management system comprising: a shieldsection comprising a cylindrical first structure positioned to receive,in a radial direction, heat generated by a heat source comprising anaircraft brake, the cylindrical first structure disposed coaxial to anaircraft wheel; and a conduction layer comprising a cylindrical secondstructure disposed coaxially to the cylindrical first structure and atleast partially radially overlapping the cylindrical first structure,thermally coupled to the cylindrical first structure, for conducting theheat in an axial direction to a dissipation apparatus, wherein thecylindrical second structure has a radius, wherein the cylindricalsecond structure comprises a carbon fiber structure configured with athermal conductivity in the axial direction greater than about 100 wattsper meter-Kelvin; and the dissipation apparatus coupled to the shieldsection, the heat dissipation section comprising an array of fins, thearray of fins comprising longitudinal fins configured such that thelongitudinal fins overlap each other on an inner radial side and suchthat a plurality of radially aligned airflow openings are formed on anouter radial side of each fin in the array of fins, wherein radiallyaligned airflow openings are not formed on the inner radial side of eachfin.
 2. The thermal management system of claim 1, wherein the shieldsection further comprises a hot side skin and a cool side skin.
 3. Thethermal management system of claim 1, wherein the conduction layercomprises a graphite structure comprising molded graphite particleshaving a mesophase pitch resin.
 4. The thermal management system ofclaim 1, further comprising an insulation layer comprising a planarcarbon fiber structure configured with a through-plane thermalconductivity less than about 10 watts per meter-Kelvin.
 5. The thermalmanagement system of claim 1, wherein the dissipation section furthercomprises a woven carbon fabric.
 6. The thermal management system ofclaim 2, wherein the hot side skin comprises at least one of analuminosilicate CMC, a SiC CMC, and a carbon composite.
 7. The thermalmanagement system of claim 2, wherein the cool side skin comprises acoating.
 8. The thermal management system of claim 2, wherein the hotside skin comprises an aluminosilicate CMC and the insulation layercomprises polysialate syntactic foam.
 9. The thermal management systemof claim 2, wherein the cool side skin comprises a polysialate matrixreinforced with at least one of a borosilicate glass and a silica fibertextile.